Niobium-titanium superconducting alloy is the most widely used superconducting material in the existing superconducting technology. The nb-ti alloy with a mass ratio of nearly l: 1 has good superconducting electrical properties and its superconducting critical transition temperature Tc=9. 5K, can operate at liquid helium temperature, it in 5T(50,000 Gs) magnetic field, the transmission current density Jc 105A/cm2(4. 2 k); The highest application field can reach 10T(100,000gs)(4. 2 k).
Superconducting wire and strip products can be obtained by the traditional melting, processing and heat treatment processes. So from the 1960s began to study, soon entered the industrial scale production. The United States produced hundreds of tons by the end of the 1970s. China also built a trial production line around the 1980s. Practical nb-ti superconducting materials are mostly simple binary alloys, containing 35% ~ 55% Nb. Parts of tantalum and zirconium can be added to improve superconductivity.
Due to the stability of superconductivity, nb-ti superconducting materials are usually made of pure copper, pure aluminum or copper-nickel alloy as the matrix material, and embedded into multiple nb-ti thin cores to form composite multi-core superconducting materials.
A superconducting wire can contain dozens to tens of thousands of nb-ti cores, with diameters ranging from 1 m. In addition, according to the use of different occasions, but also often to the multi-core wire for torsion and transposition, to reduce the loss and increase the electromagnetic stability effect.
The basic processing technology of nb-ti superconducting materials is as follows: pure titanium and pure niobium are smelted into alloy ingots by self-consuming electric arc furnace or plasma furnace, and then the ingots are extruded and unblanched by hot extrusion, and then the bars are formed by hot rolling and cold drawing. Then the nb-ti alloy rod is inserted into the anaerobic copper tube as the matrix material and compounded into a single mandril. And after several times of composite assembly, processing into multi - core Nb-Ti superconducting wire and strip.
The material must be subjected to many big cold working (working rate more than 90%) and low temperature (400 ℃) under the aging heat treatment, make superconductors have enough effective pinning center, improve the superconducting performance of superconducting material.
Due to the characteristics of zero resistance effect of superconductor without joule heat loss and the ability of nb-ti superconductor to carry high current in strong magnetic field, nb-ti superconducting material is particularly suitable for the application in the field of electrical engineering with large current and strong magnetic field.
For example: high field magnets, generators, motors, magnetohydrodynamic power generation, controlled thermonuclear reactions, energy storage devices, high-speed maglev trains, Marine electromagnetic propulsion and transmission cables.
To date, the most successful applications of nb-ti superconducting materials are the large cyclotron accelerator with a diameter of over 1km and the widely used magneto-nuclear resonance imaging diagnostic instrument in the medical sector.
